The present invention relates to a method and apparatus for measuring static and dynamic torques in a contact-free manner.
Torque pickups are known which use wire strain gauges, requiring a special cylindrical measuring body or shaft which is subjected to torsion by the occurring torque and on which the strain gauges are placed to extend at an angle of 45.degree. to the longitudinal direction. Slip rings are needed for supplying the strain gauges and for collecting the test signals. The measured shaft and the gauge are surrounded by a housing having bearings for the measured shaft. It is further known to supply the voltage for the strain gauges in their measuring position, by transformation, while the test signals are removed in a capacitative way. The costs of the electric equipment are considerable. See for example Handbuch der Industriellen Messtechnik, Vulkan Verlag 1974 (Manual of Industrial Measuring Technique, Publisher Vulcan Verlag 1974.
Inductive torque pickups are also known which comprise a special torsion stick having plunger-type armatures mounted on both its ends, which are displaced in associated coils upon a twisting of the torsion stick connected to the test piece, and which form a bridge circuit. The coils are supplied and their test signals are transmitted without a slip ring (see reference cited above).
Finally, magneto-elastic torque pickups are known which comprise three electromagnetic polar rings carrying windings and surrounding a shaft, with the intermediate winding being supplied with an AC current, and the windings on the two outer polar rings being secondary windings connected in opposition. The measured variable is the position of the zero equipotential line of the magnetic alternating field produced by the intermediate polar ring on the shaft surface. Upon the occurrence of a torque, the permeability and thus also the zero equipotential line changes so that a magnetic potential difference sets up and different voltages are induced in the secondary windings. These torque pickups do use the permeability variations for the measurement, however, the shaft must be surrounded by specially designed polar rings carrying windings (see reference cited above).